The susceptibility of cotton genotypes obtained from F6 and F7 generations to Verticillium wilt (VW) disease (Verticillium dahliae Kleb.), was studied under artificial and natural infestation during 2009 and 2010 growing seasons at the Cotton Research Institute, Nazilli, Turkey. In this study, fifteen cotton breeding lines and two control varieties were used as plant material. During the cotton growing season, foliar disease index (FDI), vascular disease index (VDI) and pot disease index (PDI) were observed in addition to seed cotton yield and some fiber quality characteristics. According to the obtained results, disease severity (DS) values observed in pot experiments were higher than field trials. In terms of DS, Tamcot CD3H— Tamcot Luxor-III, MaraÅŸ92— Tamcot Sphinx and Sayar 314— Stoneville 453-I breeding lines exhibited similar values with tolerant Carmen variety. Tamcot CD3H— Tamcot Sphinx Sayar 314— Stoneville 453-I, Sayar 314— Stoneville 453-II and Stoneville 453— Tamcot Sphinx breeding lines which gave similar DS values with tolerant Carmen variety were statistically on the same group with Carmen variety suitable to seed cotton yield. In this study, the disease tolerant breeding lines had higher fiber strength values than susceptible lines, the lowest fiber strength value obtained from Cukurova 1518 susceptible variety.